Widespread power outages affected the White House, State Department, Capitol and other sites across Washington and its suburbs Tuesday afternoon — all because of an explosion at a power plant in southern Maryland, an official said.

Many of the outages were brief, but others were longer and forced evacuations.

At the White House, backup generators kicked on when the power went out, so the interruption lasted only a few seconds. The complex quickly went back onto regular power. Electricity in the press briefing room dipped around lunchtime, briefly darkening cubicles and blackening TV screens.

Power also went out at the State Department during the daily press briefing, forcing spokeswoman Marie Harf to finish her comments to reporters in the dark. Power in the U.S. Capitol Building twice shut down briefly, then came back on by way of a generator.

Metro tweeted that several train stations were on backup power. Some traffic lights were out.

The Smithsonian tweeted that the outage affected some of its museums, and they were evacuated.

University of Maryland officials said their entire campus was affected.

D.C. Department of Homeland Security and Emergency Management spokeswoman Robyn Johnson cited the explosion at the power plant in Charles County, which is run by the Southern Maryland Electric Cooperative. About 8,000 customers in Washington were affected, Johnson said.

Utility company Pepco said it was investigating. Spokesman Sean Kelly said he didn’t have details about locations or how many customers were affected overall.

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